Allusions
The series made some allusions to the whole Kamen Rider series. Masked Rider Project as mentioned in the course of the series was said to be started on 3 April 1971. The Worm species known as Natives also first arrived on Earth on the same year. In real-life, it was the date the first Kamen Rider show aired for the first time.
Read more about this topic: Kamen Rider Kabuto